This invention relates to a wholly aromatic thermotropic liquid crystal polyester consisting of 4-oxybenzoyl units, terephthaloyl units and 4,4'-dioxydiphenyl ether units in a specified construction, to a molded product obtained by injection molding said polyester having high impact strength, and further to a blend of said polyester with so far proposed thermotropic liquid crystal polyesters.
Recently research and development have been actively carried out on polyesters forming optically anisotropic melt phase, i.e. thermotropic liquid crystal polyester, and some of them have started being industrially produced.
Since a thermotropic liquid crystal polyester has a tendency to readily orient to a great extent up melt processing, the injection molding of the polyester gives a molded product highly oriented in one direction (machine direction) having mechanical properties such as strength and elastic modulus much higher than those of molded products obtained from conventional polymeric compounds not forming liquid crystal.
It is known that among liquid crystal polyesters wholly aromatic thermotropic liquid crystal polyesters give formed products having both markedly high strengths and elastic moduli as well as being excellent in thermal characteristics.
However, injection molded products obtained from thermotropic liquid crystal polyesters are in usual cases do not always have markedly high impact strength. Further since such molded products are highly oriented in one direction, mechanical properties such as strength and elastic modulus in the direction of flow (machine direction) greatly differ from those in the direction perpendicular to that direction, showing anisotropy, and therefore they suffer a great restriction in use as product. In usual cases a filler such as glass fiber is incorporated when subjected to molding to reduce such anisotropy. It is known that in this case the impact strength of the molded product obtained decreases remarkably. Accordingly for uses where high impact strength is required a molded product obtained from a thermotropic liquid crystal polyester is not entirely suitable.
On the other hand, polycarbonates have been known as polymeric materials giving the moldings with remarkably high impact strength. However the polycarbonates are inferior in resistance to hydrolysis and resistance to organic solvent, and so when contacted with for example an organic solvent readily produce cracks, whereby the use is limited. Further the polycarbonate is, as a high performance polymer, not sufficient in heat resistance, and is not entirely good in moldability.
Further, as described before, formed products obtained from thermotropic liquid crystal polyesters have, compared to those obtained from polymeric compounds not forming liquid crystal, much higher strength and elastic modulus and lower elongation. However, for certain end-uses there is required a high strength combined with a relatively low elastic modulus or a high elongation. For example for a sealing agent for integrated circuits of electronics parts, there is desired a high flexural strength simultaneously with a low elastic modulus for rendering internal stress low.
An object of this invention is to provide a wholly aromatic thermotropic liquid crystal polyester which gives injection molded products having markedly high impact strength and heat resistance, as well as high resistance to solvents.
Another object of this invention is to provide a blend of a melt-processable thermotropic liquid crystal polyester which gives various formed products which are, while superior in strength, relatively low in elastic modulus, relatively high in breaking elongation, and excellent in toughness, as well as excellent in thermal characteristics.